The main questions in human tumor immunology continue to be whether tumor cells express cell surface antigens absent from all normal cell types and whether the immune system is able to recognize these new antigens and mount an immune response against them.
To answer these questions, the serological response of cancer patients against their tumor cells has been studied by autologous typing, where the patients' sera are tested on the autologous cultured tumor cell line and absorption tests are done to determine the specificity of the reactivity. Autologous typing has been used to study the sera of patients with melanoma, astrocytoma, renal cancer and leukemia. The antigens recognized by the patients' sera can be grouped in three different categories. Class 1 antigens or unique antigens only expressed by the autologous tumor cell line; Class 2 antigens expressed by the autologus tumor and other allogeneic tumor or normal cells of the same type or related embryologic origin (Class 2 antigens turn out to be differentiation antigens); Class 3 antigens widely distributed and found in the autologus tumor and also in allogeneic tumor cell lines and normal cells of varied embryologic origin.
Although all three classes of antigens are of interest because of the ability to be autoimmunogenic, Class 1 antigens are particularly interesting because of their very restricted distribution.
The characterization of the unique antigens has been hampered by the small number of patients who develop these antibodies, the low titer of the sera and the inability to immunoprecipitate the antigen from cultured cells.